I lived in Leith, Edinburgh, Scotland, where Trainspotting is based. The area has a methadone clinic on Great Junction Street, also (not so) affectionately called "Great Junkie Street." The area was decimated by the HIV epidemic in the 90s, but the area is now gentrifying, with beggars sitting outside of high-end eateries and stores on Leith Walk. While there are many similarities to Seattle, it's very obvious America takes a lot less care of its' mentally ill, addicted, uneducated and poor, although Seattle clearly does a lot better than many places in the US.

Seattle's problem is exacerbated by the fact that the city has effectively legalised heroin, crack and meth by raising the bar on possession, and the police have a catch and release policy, without any actual treatment given. Numbers of addicts living here are also up because neighboring cities' police departments will issue non-extraditable misdemeanor arrest warrants for them, effectively turning Seattle into a dumping ground.

Not unique to Seattle or the US, police don't to waste their time on minor crimes. E.g. <$1000 in theft/damage, when a shoplifter fights store security but doesn't use a weapon, etc. This is because they know the county prosecutors will not file felony charges. Thus criminals target accordingly without fear of felony prosecution. I highly recommend this Reddit post by an anonymous Seattle cop explaining this.

Washington state also trails the nation in mental health treatment and has a high prevalence of mental illness. (Reference.)

I grew up in Perth, and for 5 years lived in a relatively dangerous area, Carlisle, between the Burswood Crown Casino and notorious Oats St Station. I felt unsafe on public transport more frequently than in Seattle, but I downright dread downtown bus changes where homeless people congregate. Overall, I would say I feel unsafe here enough that it is a major con of living here, and it's something I am forced to warn visitors, or prospective migrants about. Sorry Seattle and America - get your things together and help your fellow man like lots of other countries manage to.